In this seven year cooperative agreement we propose to test a school-based intervention to prevent type 2 diabetes (T2D) in children and adolescents. Obesity is increasing markedly in American youth, and this increase, which is already accompanied by an explosion in the incidence of T2D in youth, is expected to further increase unless effective interventions can be instituted. The proposed study will test an environmental and lifestyle intervention that could serve as a model for long-term school-based interventions to reduce obesity and prevent T2DM in schools throughout the US. The specific aim of this proposal is to test a longitudinal school-based intervention to prevent T2D and insulin resistance in elementary and middle school youth. The primary focus of the intervention will be to add a prescribed physical activity program to the school curriculum for one, two or three years, and to modify access of youth to soft drinks at school. Additional components of the intervention will be intermittent classes to increase knowledge and influence attitudes about physical activity, nutrition, and diabetes, and some involvement of the parents. Elementary and middle schools will be randomly assigned to the intervention or control group. Participants will be 3939 youth with parental consent and personal assent. Data will be collected at baseline and annually for four more years. A subset of youth at greatest risk for T2D (body mass index > 85th percentile of national norms and T2D in first or second degree relatives and fast insulin > 25 micrograms/ml) from both groups will receive an oral glucose tolerance test. All data will be collected at the study schools. The primary outcome of the study will be the development of T2D (fasting glucose > 126 mg/dl) or impaired fasting glucose (fasting blood glucose 110- 125mg/d). We hypothesize that, as compared with children in the control schools, fewer youth in the intervention schools will develop T2D or impaired fasting glucose. Secondary outcomes of interest that also will be addressed by the proposed study include: 1) Insulin resistance, determined with a combination of factors that will include high fasting serum insulin levels, insulin sensitivity index, acanthosis nigricans, hypertension, specific dyslipidemias (low high density lipoproteins [HDL-C] and high triglycerides [TG]); 2) General obesity (body mass index and sum of skinfolds); 3) Central obesity (waist and hip circumferences; 4) Aerobic power (VO2max.); 5) Health Behaviors, specifically, physical activity and eating habits; and 6) health knowledge about ways to prevent T2DM. We hypothesize that, as compared with children in the control schools, fewer children receiving the intervention will exhibit insulin resistance, fewer children will show general and central obesity, and more children will have improved their aerobic power (pVO2), physical activity, eating habits, and health knowledge. Since the proposed study is a cooperative agreement involving multiple sites, the actual aims, variables and procedures will most likely be modified during the initial planning year.